A Kalman Filter-based Doppler-smoothing of Code Pseudoranges in GNSS-Challenged Environments

Mojtaba Bahrami and Marek Ziebart

Abstract:	Motivated both by the continual availability and the centimeter-level precision of the receiver generated (raw) Doppler frequency shift measurements, even in severe urban canyons, in this paper a Kalman filter-based combination procedure of the noisy code pseudoranges and the Doppler shift measurements is suggested and its benefits are examined. The objective is to smooth the code pseudoranges and push the precision of the code-based or both code- and carrier-based positioning and navigation solutions in GNSS-challenged environments. It is shown that the proposed Kalman filter-based Doppler-smoothing of code pseudoranges offers a modest improvement and in GNSS difficult environments is more robust and effective than that of the traditional measurement domain carrier-phase smoothing of code pseudoranges (e.g. the Hatch filter). While carrier-phase tracking is continuous and free from cycle-slips, the Hatch filter with an optimal smoothing window-width can effectively suppress receiver noise and short-term multipath on code pseudoranges. However, the effectiveness of the Hatch filter is limited in urban areas and difficult environments, because carrier-phase measurements deteriorate easily and substantially due to blockages and foliage and suffer from discontinuities, cycle-slips and other measurement anomalies. On the other hand, a receiver can generate Doppler shift measurements with centimeter-level precision as long as a signal is present. By taking advantage of the availability and the precision of raw Doppler measurements to “average out” the code pseudorange noise, our early experimental results clearly show the improvements gained by the Doppler-smoothing approach in GNSS-challenged environments compared to that of the traditional carrier-phase smoothing of code pseudoranges. The Kalman filter approach is an efficient and elegant implementation of the Doppler-smoothing method where it can run as a continuous process in the receiver from the first epoch (or post-processing software, but then without the real time advantage). Hence, this filter implementation allows real-time operation of the Doppler-smoothing approach.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2362 - 2372
Cite this article:	Bahrami, Mojtaba, Ziebart, Marek, "A Kalman Filter-based Doppler-smoothing of Code Pseudoranges in GNSS-Challenged Environments," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 2362-2372.
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